1. Field of the Invention
The present invention relates to a high-frequency input circuit such as that often used in television tuners, which has a circuit for switching high frequencies and a variable attenuation circuit for controlling the amount of signals transmitted and more particularly to such a high-frequency input circuit including P-I-N diodes which serve as switching elements in the high-frequency switching circuit and also as variable resistance elements for controlling the amount of signal transmission.
2. Prior Art
Conventional high-frequency input circuits for such devices as television tuners have a high-frequency switching circuit between two inputs and a variable attenuation circuit for controlling the amount of input signals transmitted. The switching circuit typically has switching diodes, and the variable attenuation circuit often has P-I-N diodes, with the circuits arranged independently for each input. Accordingly, the number of diodes used is quite large, resulting in a large losses due to diode resistance in the forward direction. The greater the number of diodes, the greater the number of parts necessary for applying bias voltages to the diodes, with the result that the overall circuit arrangement is expensive to construct.